I have designed a board for EMX, and I wonder what battery should I use (connect to Vbat)to allow the board to keep the correct date several years :
-According to LPC2478 documentation and to amperemeter measure, the current is approx. 20 microAmps, so for example, if I use a small CR1216 25mAh coin cell, the RTC should fail in less than 2 months : (25000 / 20 ) = 1250 hours = 52 days < 2 months
-So I am currently looking for biggest batteries for RTC : (even biggest coin cells are not enough) Those 2500 mAh 3.6V seems OK for nearly 15 years : http://www.farnell.com/datasheets/1443075.pdf
I am just surprised that a coin cell is not enough, because coin cells are used in old computers, and I guess that they keep the correct date several years… Do I miss something?